How to check a thyristor if you are a complete dummie? So, first things first.
The operating principle of a thyristor is based on the operating principle of an electromagnetic relay. A relay is an electromechanical product, while a thyristor is purely electrical. Let's look at the principle of operation of a thyristor, otherwise how can we check it then? I think everyone rode the elevator ;-). By pressing a button on any floor, the elevator's electric motor begins its movement, pulls a cable with a cabin with you and your neighbor Aunt Valya, about two hundred kilograms, and you move from floor to floor. How did we use a tiny button to raise the cabin with Aunt Valya on board?
This example is the basis of the operating principle of a thyristor. By controlling a small voltage on the button, we control a large voltage... isn't this a miracle? Moreover, there are no clicking contacts in the thyristor, like in a relay. This means that there is nothing to burn out and under normal operating conditions such a thyristor will serve you, one might say, indefinitely.
Thyristors look something like this:
And here is the circuit designation of the thyristor
Currently, powerful thyristors are used to switch (switch) high voltages in electric drives, in installations for melting metal using an electric arc (in short, using a short circuit, resulting in such powerful heating that the metal even begins to melt)
The thyristors on the left are installed on aluminum radiators, and tablet thyristors are even installed on water-cooled radiators, because a crazy amount of current passes through them and they switch very high power.
Low-power thyristors are used in the radio industry and, of course, in amateur radio.
Let's understand some important parameters of thyristors. Without knowing these parameters, we will not catch up with the principle of testing a thyristor. So:
1) U y– – the lowest constant voltage on the control electrode, causing the thyristor to switch from a closed state to an open state. In short, in simple language, the minimum voltage on the control electrode, which opens the thyristor and the electric current begins to flow quietly through the two remaining terminals - the anode and cathode of the thyristor. This is the minimum opening voltage of the thyristor.
2) U arr max– reverse voltage, which a thyristor can withstand when, roughly speaking, the plus is supplied to the cathode and the minus to the anode.
3) I OS Wed –average current value, which can flow through the thyristor in the forward direction without harm to its health.
The remaining parameters are not so critical for beginner radio amateurs. You can get acquainted with them in any reference book.
Well, finally we move on to the most important thing - checking the thyristor. We will check the most popular and famous Soviet thyristor - KU202N.
And here is his pinout
To test the thyristor, we need a light bulb, three wires and a DC power supply. On the power supply we set the voltage for the light bulb to light up. We tie and solder wires to each thyristor terminal.
We supply “plus” from the power supply to the anode, and “minus” to the cathode through a light bulb.
Now we need to apply voltage relative to the anode to the Control Electrode (CE). For this type of thyristor U y– unlocking constant control voltage more than 0.2 Volt. We take a one and a half volt battery and apply voltage to the UE. Voila! The light bulb came on!
You can also use multimeter probes in continuity mode; the voltage on the probes is also more than 0.2 Volts
We remove the battery or probes, the light should continue to light.
We opened the thyristor by applying a voltage pulse to the UE. Everything is elementary and simple! In order for the thyristor to close again, we need to either break the circuit, that is, turn off the light bulb or remove the probes, or apply reverse voltage for a moment.
You can also check the thyristor using. To do this, we assemble it according to this diagram:
Since there is voltage on the multimeter probes in the continuity mode, we supply it to the UE. To do this, we close the anode and the UE between each other and the resistance through the Anode-Cathode of the thyristor drops sharply. In the cartoon we see a 112 millivolt voltage drop. This means that it has opened.
After releasing, the multimeter again shows infinite resistance.
Why did the thyristor close? After all, the light bulb in our previous example was on? The thing is that the thyristor closes when holding current becomes very small. In a multimeter, the current through the probes is very small, so the thyristor closed without voltage from the UE.
There is also a diagram of an excellent device for testing a thyristor, you can look at it in this article.
I also advise you to watch the video from ChipDip about checking the thyristor and holding current:
The New Year is coming - and now Christmas tree decorations and garlands come out of the boxes. And if the toy is simply hung in the place chosen for it, then there are various accidents with the garlands. This is especially true for cheap options. Anyone who has ever repaired this miracle of technology knows that the Chinese garland, whose circuit is simple, has some features.
Most often, Chinese craftsmen are attracted to New Year's decorations by their attractive price (from 150 rubles per piece) and bright lights that flash in several modes. Four types of light bulbs, and sometimes LEDs, are pleasing to the eye and wallet. True, after a while one or several colors stop burning. There may be several reasons, but the fact remains that the garland no longer works 100%.
If the product is damaged, it is not necessary to replace it with a new one. Although it is customary to enter the New Year with everything new, our hands are not made for boredom. Is it really difficult to change a burnt out light bulb? The point here is not the price or the time spent on repairs. It's a matter of principle. And every person who decides to repair a Chinese garland for the first time begins to be surprised.
The most unpleasant surprise during repairs is thin wire strands. You begin to wonder how it all works and has not yet fallen apart. Both the price of the product and the reliability of operation become clear. This is the Chinese garland. Scheme, repair and search for gaps - this is your future fate. The wiring connection is naturally the weakest point. Therefore, you should start searching for a gap with the switching box.
In addition to surprisingly thin wiring, the Chinese product can please you with the quick failure of the thyristors that control the color lines, as well as the main controller. To replace faulty elements, you most often have to look for domestic analogues or redo the entire circuit.
Let's consider some of the possible cases when the Chinese garland circuit is not needed. From the electrical engineering course, only 2 problems associated with electrical problems are known: short circuit and open circuit. In the case of a non-working garland, you need to look for a gap. Let's say the blue light is off. There are 2 options possible:
Now you need to find a break or a burnt out light bulb. As a rule, a visual inspection will help us with this. Most often, the gap is visible to the naked eye, and the repair quickly ends. To connect the two ends of the wire, you don’t even need to have a soldering iron on hand - simple twisting helps. It is imperative to wrap it with electrical tape.
Attention! Any repair of an electrical product is carried out without connecting to the network.
If the gap is not visible, you should pay attention to the box with the button. The Chinese garland, the design of which does not differ from the standard one, has a control unit in a flat box. By unscrewing 2 or more screws, you can see a small printed circuit board with several elements. It comes with 2 wires from the plug: phase and neutral, as well as 4 wires with light bulbs of four different colors. Breaks most often occur at the junction of wire strands.
A number of malfunctions are associated with malfunction. Here, the mode switching button itself may fail. This problem can be “cured” by cleaning the contacts or completely replacing them. A Chinese garland, the circuit of which is standard, necessarily includes a controller. It can also go bad and can be replaced too. The weak link can be any of the 4 thyristors - one for each color.
To replace faulty elements, Chinese colleagues offer their own. The problem is that lamps become outdated quite quickly, and finding the right Chinese-made version can be problematic. In this case, the domestic element base comes to the rescue. The most important thing is to choose the right analogue.
To select an analogue of the desired element, it is important to know the parameters of the Chinese product. The PCR406J transistor is often searched for on forums. The Chinese garland, the diagram of which is made on such elements, is familiar. Only the desired element actually turns out to be a thyristor, and its Russian analogue MCR100 is almost identical in parameters.
What to do if no breaks are found? The design of a Chinese garland is simple. All light bulbs are connected to each other in series. This means that if the blue line is not lit, you need to find at least one burnt out one. There are two options.
The second method can be avoided if you use a multimeter with thin needles attached to the ends of the probes. However, the conductor strands used in Chinese products are so thin that they can be torn even by a needle.
It happens that you don’t have a second damaged garland or a new light bulb at hand. In this case, you can simply connect the two ends together. This is fraught with an increase in voltage on the remaining light bulbs, since according to the laws of electrical engineering in a series circuit, the voltage is divided equally. But if you remove one or two elements, this will not greatly affect the service life. Despite the fact that they are Chinese, everything works on general principles.
Such products have recently become widespread. In this regard, low-power elements appeared on the garlands instead of light bulbs. The Chinese scheme differs little from the standard one. But, given the fact that the LED is designed for a much lower voltage, each of them will have a resistor in the circuit for a 220 V network. In another embodiment, a step-down transformer will be implemented at the system input.
In addition to the usual circuit, where the elements are arranged in series, there is a circuit of a Chinese garland with LEDs placed in parallel. With this option, even the burnout of several light elements at once will not introduce dissonance into the overall picture.
A Chinese garland, the circuit of which is built on LEDs, has a number of advantages.
LED Chinese garlands are very convenient to use to decorate the outdoor part of the house. Due to their high moisture and frost resistance, such products will please the eye for a long time without repair.
When buying such a product, it is not always possible to please yourself and your loved ones with high-quality jewelry. Sometimes, behind bright lights and an attractive price, a rather simple and cheap Chinese garland is hidden. Its circuit will be easy to study and convenient for applying electrical skills. Repairing a product can also bring moral satisfaction. Everyone determines for themselves whether it is worth the time and effort. Or maybe it’s better to immediately take the more expensive option? After all, even Chinese garlands for a high price are much better quality than their cheap “compatriots”. The choice is yours!
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